1. Field of the Invention
This invention relates to a sintered friction bearing for motors and gears with a bearing surface, which has a bearing bore and can have a lubricant from lubricant depositories in the bearing. The bearing bore has alternating highly compressed, small-pored bearing surfaces distributed over the circumference and slightly compressed, open-pored lubricant depositories from one front face to the other front face of the bearing.
2. Description of Related Art
A sintered friction bearing is known from the German Publication xe2x80x9cTribologie+Schmierungstechnikxe2x80x9d[Tribology and Lubrication Technology], vol. 45, 1/1988, pp. 47/48. The lubricant depositories are cut in the form of grooves of triangular cross section into the bearing bore of the sintered body, while the bearing surfaces between the grooves are compressed by roll drafting. These lubricant depositories are able to receive lubricants, which during operation are exuded from the sintered bearing, for example are displaced from the not so highly compressed areas. Because the grooves are axially oriented and are arranged at some distance from each other and also have a large width, the lubricating effect is not evenly distributed over the entire bearing surface of the bearing bore, and is insufficient in the start-up phases in particular.
This also correspondingly applies to a sintered bearing in accordance with U.S. Pat. No. 5,704,718, wherein the lubricant depositories are formed by large, U-shaped grooves each having a groove bottom set off by a larger diameter in comparison with the bearing surfaces. The lubricant stored in these grooves during stopping cannot effectively aid lubrication during the start-up phases of the operation. The lubricant depositories first must be filled with lubricant before they are an effective part of the lubrication of the shaft.
It is one object of this invention to improve lubricating action of lubricant depositories in a sintered friction bearing of the type mentioned above but in such a way that, regardless of the installed position of the bearing, at least a portion of the circumferential surface of the shaft is always connected with a lubricant depository.
In accordance with this invention, this object is attained with lubricant depositories embodied as grooved structures with at least two longitudinal grooves, which are inclined at an acute angle with respect to the center axis of the bearing bore from front face to front face of the bearing.
Because of the inclined orientation of the grooved structures, the strips of bearing surfaces between the front faces of the bearing can be lined up with their ends, so that a shaft inserted into the bearing bore is always in at least partial contact with a lubricant depository, over the entire circumference of the shaft. Thus the lubricating action of the lubricant depository is considerably improved, and the sintered bearing is sufficiently lubricated, regardless of its position with respect to the shaft.
If in accordance with one embodiment, the longitudinal grooves of the grooved structures are closed in the area of their front faces. The lubricant received in the longitudinal grooves of the grooved structures cannot exit from the bearing and is completely available for lubricating the shaft.
In accordance with a simple embodiment, the longitudinal grooves can be closed by deformed portions of the sintered bearing.
In accordance with a further embodiment, distribution of the lubricant over the entire circumferential surface of the shaft can be improved because the ends of adjoining grooved structures overlap at least partially at the two front faces.
Cutting the grooved structures into the bearing bore is simplified because the grooved structures are arranged at the same distance from each other and therefore in the same angular range, so that the angle position of the cutting tool can be maintained.
The grooved structures are completed because the longitudinal grooves are separated from each other by groove caps in non-bearing contact with the shaft inserted into the bearing groove, but at least partially contact the shaft, for transferring lubricant. Thus the lubrication of the shaft in the start-up phases of operation is improved because of the lubrication by the porous groove caps.
In one embodiment the size of the groove structures is distinguished because the longitudinal grooves have a depth of up to 0.5 mm and a width in the area of the bearing bore of 0.30 to 0.50 mm, wherein the radii of the longitudinal grooves are at least 0.05 mm, and the groove caps are of the same size in a laterally reversed manner.